WB update: 4V output

[bcroe at juno.com]

All,

I'd better add a note to my last post that the exact values
were for R9 and R10 connections to VR3 NOT reversed.
The Ip signal is not symetric so if you reverse them it
will be necessary to change the offset voltage applied
to R11 (100K) from 0.811V to 0.189V.  This can be done
by replacing R11 with a 102.42K resistor from U3A + to
actual ground, and a 4.233 meg resistor from U3A + to
8 volts

Marvin, 

To get a 0 to 4 volt output I'll assume we are reversing 
the connections of R9 and R10 to VR3, but lets leave
them 22K for more gain.  Lets again assume an Ip
current variation of 3.97 ma through a VR3 of 151.6 ohms
will produce a signal of 0.601V.  To get this up to 4V
we need R11 and R12 to be 4/.601 times 22k (R9 and
10), or 146.4K.  The bottom of R11 will be moved from
virtual ground to an actual 0.752V source.  Or replace
it with a 110.4K resistor from U3A + to actual ground,
and a 1.064 meg resistor from U3A + to 8V

Once again, if you go for the 11:1 to 22:1 range instead
of the 10.62:1 to 17:1 on Bruce Plecans' chart on the 
Web site, you will need to modify the above a bit.  I
am still looking for an explanation of A/F calibration
procedures.  Bruce Roe


On Thu, 29 Mar 2001 20:03:40 -0000 "The Punisher"
<punisher454 at hotmail.com> writes:
> Another thing anybody working on the WB driver might consider in 
> addition to 
> a 0-1v output is a 0-4 volt output for easy interfacing to an ADC 
> without 
> the need for an op-amp.
> When I made my pic controlled LCD unit for a std O2 sensor, the 0-1v 
> range 
> was a pain in the butt. The LTC1298 that I was using was ALOT 
> happier with 
> 0-4v than 0-1v. accuracy and noise reduction were vastly improved 
> with a 
> wider voltage range.
> In testing I had a 0-1v and a 0-4v voltage source. The LTC 1298 is 
> 12 bit 
> but I was able to get away with 10 bit sampling at 0-4v with as 
> opposed to 
> 12 bit at 0-1v. I tried several op-amp and voltage reference 
> combinations, 
> but still had the most stable & noise resistant results with 0-4v as 
> opposed to 0-1v.

> 
> Keep up the excelent work

> Marvin Fugate (The Punisher)

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